Recent progress of aqueous and organic/aqueous hybrid electrolytes for low-temperature rechargeable metal-ion batteries and supercapacitors

Aqueous rechargeable metal-ion batteries (ARMBs) and supercapacitors have received extensive research attention owing to their intrinsic high ionic conductivity, high safety, low cost, and eco-friendliness. The ever-growing industrial applications of energy storage systems further call for batteries with wide working temperature ranges, whereas the study on the low-temperature performance improvement of ARMBs remains a barely explored area compared to their organic counterparts. As the media component determining transportation of charge carrier ions, electrolytes substantially impact key performance metrics of ARMBs. Herein, critical electrolyte issues dominating the low-temperature performance of ARMBs are discussed and summarized. Recent advancements in low-temperature aqueous/hybrid electrolytes are comprehensively reviewed, encompassing optimization of concentration and species of salt, introduction of anti-freezing additives or organic co-solvents, and utilization of hydrogel matrix. In general, most low-temperature aqueous electrolyte design strategies rely upon the eutectic properties of solutions and solvation network modulation. Future perspectives are proposed in the final section to inspire novel designs and discoveries devoted to high-performance ARMBs operating in low-temperature conditions.